1. Field of the Invention
The present invention relates to a mechanism for automatically modulating fuel delivery to an engine. More specifically, the present invention relates to such a mechanism for synchronizing and/or reducing shifting shocks of a transmission.
2. Description of the Prior Art
It has been previously proposed to automatically modulate or vary the speed of an engine during shifting modes of a transmission in an effort to simulate what is done by an experienced driver during manual shifting. For example, U.S. Pat. No. 3,736,806 proposes increasing fuel delivery to an engine during manual shifting of a mechanical transmission; U.S. Pat. No. 3,834,499 proposes both increasing and decreasing fuel delivery to an engine during automatic shifting of a mechanical transmission; and U.S. Pat. No. 4,226,141 proposes decreasing fuel delivery to an engine during automatic shifting of a transmission to facilitate synchronization of the transmission and to reduce shifting shocks.
The prior art mechanisms for modulating engine speed during shifting modes of a transmission have had several disadvantages. Most have been on/off type mechanisms which have not provided smooth, precise changes in engine speed and torque and, therefore, have provided less than optimum synchronizing and shift shock results. Some have been incorporated directly into fuel control devices and therefore have required complex and costly redesign of the fuel control devices. Some have operated directly on throttle pedal linkages with resulting mechanical feedback or physical movement of the throttle pedal. This feedback or movement, which is noticed by the operator, is disagreeable and interferes with proper and effective control of the vehicle.
Further, with respect to optimum synchronizing and shift shock, the prior art mechanisms have not readily provided the many different precise degrees of fuel delivery change necessary during shifting modes of a transmission. For example, precisely regulated, ramped, incremental increases and decreases of fuel delivery can greatly reduce shifting shocks felt by a vehicle operator, reduce torsional oscillations in the vehicle drivetrain, reduce synchronizing time, reduce energy consumed by synchronizing devices, and reduce impulse forces on jaw clutches.
Further, with respect to mechanical feedback or physical movement of the throttle pedal, even though a modulation mechanism may not physically move the throttle pedal during throttle modulation, the mechanism may cause objectionable force changes on the throttle pedal if the spring biasing the throttle system toward idle is not properly positioned. These force changes, though not as disagreeable as physical movement of the throttle pedal, are nevertheless distracting to a vehicle operator.